Arc tube system



' M r h 18, 1.941. D. D. coFF'm' 2,234 963 ARC TUBE SYSTEM Filed July14, 1939 a INVENTOR.

DAVID D. Cor-FIN,

ATTY.

Patented Mar. 18, 1941 UNITED STATES PATENT. OFFICE ARC TUBE SYSTEMApplication July 14, 1939, Serial No. 284,501

15 Claims.

This invention relates to an arc tube system, and more particularly tosuch a system in which two controlled arc tubes are connected inverselyin order tosupply a controlled alternating our- 5 rent load, such as aresistance welding load.

In alternating current systems of this general nature, particularly inthe case of resistance welding loads, it is desirable that if one of thearc tubes fails to conduct current upon the application of an ignitingimpulse to its igniting electrode, the other are tube shall also beprevented from starting. If this is not done, the current supplied tothe load hasa substantially direct current component which is usuallydisadvantageous, especially when undesired magnetic saturation ofmagnetic elements in the load circuit may result.

An object of this invention is to devise means responsive to the absenceof conduction in either tube for deenergizing the firing circuit of theother tube.

The causes which prevent a tube from firing upon the application of anigniting impulse to the igniting electrode are often temporary incharacter, and therefore it is often desirable to repeat the applicationof igniting impulses to the tube which fails to fire. Another object ofthis invention is to devise means for doing this, which means, however,prevents igniting impulses from being supplied to said other tube aslong as the first tube fails to fire.

The foregoing and other objects of this invention will be bestunderstood from the following description of an exempliiication thereof,reference being had to the accompanying drawing, wherein:

Fig. l is a diagrammaticrepresentation of a circuit embodying thepresent invention; and

Fig. 2 is a curve illustrating the operation of the system shown in Fig.1.

The embodiment illustrated consists of two are tubes I and 2, preferablyof the mercury pool cathode type. These tubes contain mercury poolcathodes 3 and 4, and anodes 5 and 6, respectively, and are providedwith igniting electrodes I and 8. Although these igniting electrodes maybe of any type which initiate an are on the mercury pool cathode bymeans of an igniting impulse supplied thereto, they preferably are ofthe type which consists of a conductor separated from the mercury poolby aninsulating layer which preferably consists of glass. Moreparticularly these igniting electrodes may be of the form described andclaimed in the copending application of Percy L. Spencer, Serial No.259,355, filed March 2, 1939,

for an improvement in Arc starting devices. In igniting electrodes ofthis kind, the glass layer on the igniting electrode conductor is incontact with the surface oi. the mercury pool, and the arc tends to format some such point of contact. The upper ends of the electrodes 1 and 8may be left exposed to the discharge so as to provide discharge paths inparallel with the respective cathodes and igniting electrodes.

Two alternating current lines 8 and ID are con- 10 nected to supply asuitable alternating current load which may consist of a transformer Hhaving a primary l2, a secondary l3, and a load ll. In the particularsystem shown, the load Il may consist of a resistance welding load. Theare tubes I and 2 are interposed in one of the conductors Iii in orderto control the flow of current to the load. In order to permitalternating current to flow through the tube system, the two tubes arereversely connected by means of the 2 crossed conductors l5 and i6. Ifthe tubes i and 2 are conducting, current pulses of one polarity willflow through tube I, and current pulses of the opposite polarity willflow through tube 2, thus delivering alternating current to the load.If, however, tubes l and 2 are non-conducting, the load is deenergized.

Igniting transformers ii and iii are provided to supply ignitingimpulses to the igniting electrodes i and 8, respectively. Theseigniting transformers are provided with secondary windings i9 and 28.The secondary winding !9 is connected between the igniting electrode 7and "the cathode pool 3, While the secondary winding 2b is connectedbetween the igniting electrode 8 and the cathode pool 3. Thetransformers i! and iii are also provided with primary windings 2i and"2 2 which are supplied with igniting voltage impulses through a controlcircuit which is energized from atransformer 23 having a primary winding24 connected directly across'the tubes l and 2. For this purpose the twoends of the primary winding 24 are connected respectively to the twoconductors l5 and it. The transformer 23 also has a secondary winding 25which supplies primary windings 2i and 22 with unidirectional impulsesthrough a rectifying bridge. A pair of control contacts 26 areinterposed in one of the conductors leading from the secondary winding25 to the rectifying bridge. These control contacts may be operated froma control pushbutton or from some suitable timing arrangement.

The rectifying bridge comprises four rectifiers 21, 28, 29 and 30,preferably of the copper oxide type. The primary windings 2| and 22constitute two outerlegs of the bridge, while a conductiveconnection 3i,extending from a point between the rectifiers 2i! and 28 to a pointbetween the rectifiers 29 and 3B, constitutes the central leg of saidbridge. Included in the central leg ii is a relay armature 32 whichnormally completes the connection between a pair of contacts 3-333.

The armature 82 forms part of a relay 3% which is provided with anoperating coil 35. Said operatins coil 35 is also in series with thecontacts 23383 in said central leg 3 l. The polarities of the rectiflersill-do are such that rectifiers El and 3t allow impulses of one polarityto pass through the primary winding 22, while the rectifiers 23 and 29allow impulses of the opmsite polarity to pass through the primarywinding 2i.

Connected directly across the tubes 6 and 2 is a series circuitconsisting of a resistance 36 and a condenser 87!. This circuit is toenable the incipient arc spots initiated-by the igniting impulsessupplied to the igniting electrodes 71 and 8 to progress rapidly intotrue arc spots irrespective of the nature of the main load. This featureis more fully described and claimed in the copending application ofWilcox P. Over-beck, Serial No. 271,679, filed May 4, 1939, for animprovement in Arc tube systems.

The operation of the system described above can be best understood byreferring to the curves shown in Fig. 2. These curves do not purport toshow quantitativel the current and voltages involved. However, they dorepresent ina general qualitative manner the operation of the system. InFig. 2 the sine wave a represents the line voltage which appears acrossthe corn ductors 9 and id. The curve b represents the load currentflowing to the primary winding it. In the systems which arecontemplated, particularly resistance welding systems, the current blags the voltage a, and in the particular instance shown, this lag isabout 60 degrees. As the current passes through zero, one of the arctubes l or 2 goes out, and normally the other tube starts immediately,delivering smooth alternating current to the load. The curve 0, whichrepresents the voltage across the tubes l and 2, shows that when one ofthe arc tubes goes out, the voltage across said tubes rises very rapidlyto the instantaneous value of the line voltage at that particularmoment. The system is so arranged that this voltage impulse istransmitted through the firing circuit so as to ignite the previouslyidle tube, which thereupon immediately starts conducting current so thatthe voltage across the tube then drops to the relatively low value ofthe tube arc drop. This operation takes such a short time that the risein voltage across the tube lasts for a very short time, and thereforethese voltage impulses are represented in curve by vertical lines. Ofcourse it is to be understood that this change does occupy some timeinterval which, however, it is impractical to illustrate in Fig. 2. Itwill be seen, therefore, that the voltage across the tubes 8 and 2supplies voltage impulses at exactly the right moment in order toalternatively fire the tubes l and 2 so as to cause the alternating loadcurrent b to flow smoothly through said tubes. connected directly acrossthe tubes l and 2 has this voltage wave 0 impressed upon it. This samevoltage wave 0 is therefore impressed through the secondary winding 25upon each or the primary windings 2i and 22 connected in series withtheir respective rectifiers 28 and 28.

conductive connection 35,

The primary winding 26 which iswinding 2i, while voltage impulses of theopposite polarity pass through primary winding 22. Thus the impulses ofthe voltage wave 0 which lie above the zero axis are impressed upon thelgniting electrode 7, for example, while those voltage impulses of thewave 0 which lie below the axis are impressed on the other ignitingelectrode 8, for example. The polarities of the windlogs on thetransformers ii and it are so chosen that the voltage impulses suppliedto the igniting electrodes 1 and 8 are primarily positive with respectto the associated cathodes 3 and 3.

When the control contacts 28 are closed, the igniting circuit isenergized and the tubes l and 2 conduct current substantially asdescribed above. If, however, one of the tubes l or 2 fails to becomeconductive upon an igniting impulse being supplied to its associatedigniting electrode or 8, the rela 3G is operated toopen the connectionbetween the contacts 33-33. This action may be described in connectionwith the curves shown in Fig. 2. It will be seen that during normaloperation of the system, the voltage which is impressed upon theoperatingcoil 35 of the relay 3i is represented by the complete curve 0,since both polarities of the curve 0 passed by the rectifying bridgepass through the central The only portions of the curve c which have anysubstantial magnitude are the vertical portions. However, these verticalportions, as previously described, are of very short duration, such thatthey are insufilcient to cause the coil 35 to operate the relay 36. If,however, upon the occurrence of an igniting impulse at one of theigniting electrodes, the associated tube does not become conducting, thevoltage across the tubes instead of falling to the relatively low valuerepresented by the voltage drop of the tube, continues to follow theline voltage a.

Therefore, upon the failure of a tube to become conducting, coil 35 issupplied with a considerable voltage which persists throughout theremaining portion of the voltage wave. The relay 34 is'so designed thatif this voltage persists for a sufficient period of time, the coil 35will operate the relay 34, thus opening the contacts 33-453. The relay34 is so designed that this operation may occur at some such point as pon the curve a in Fig. 2. When the relay 3 3 is operated and thecontacts 33-33 are opened both primary windings 2i an 22 aredeenergized, and thereafter no impulses are supplied to the ignitingtransformers ii and it until the contacts 33-33 are again closed by thearmature 32. It will be noted, however, that after the initialoccurrence of the voltage impulse to the associated igniting electrode,as represented by the left-hand vertical portion of the curve c, voltageis continued to be supplied to the associated igniting transformer untilthe point pis reached,

due to the delay-in the operation of the relay 3! In many instances,although a tube may fail to ignite, upon the supply of a short ignitingimpulse thereto, this failure may be due to a temporary cause, and ifthe igniting voltage persists until said temporary cause is removed, thetube may then ignite properly. The period of delay between the initialapplication of the igniting voltage and the point p affords theassociated tube an opportunity to ignite under conditions of this kind.In some instancesit may be desirable to provide for a greater increasein flow of current through coil 35 upon the failure of a tube assaoea tofire. For this reason the cores of transformers i7 and II are soproportioned as to become saturated if the voltages supplied to them aresubstantially larger than a normal igniting impulse. Thus upon thefailure of one of the tubes to fire, the associated transformer II or itwill saturate, lowering its impedance and permitting a greatly.increased current to flow through coil 8|. This insures a positive andreliable action of the relay 34.

When the relay It has been operated at the point p, it persists in itsoperated or open position for another delay period which may end, for

period in which the anode of said tube becomes positive. Thus, if thecauses which prevented the tube from firing were temporary and existedthroughout the previous positive half cycle, the reapplication of anigniting voltage to said tube may permit said tube to fire normally ifthe tube is then in a condition to do so. If, however, the tube fails totire, relay 34 is again energized to prevent the other tube from beingignited.

It is usually desirable to provide some adjustment for the periods ofdelay to which the operation and release of the relay II are subjected.Such an adjustment may be afforded, for exam ple, by a tension spring38, the tension of which may be adjusted by an adjusting screw 30. Theadjustment also may be afforded by an adjustable impedance, such as avariable resistance ll placed across the coil 3!. These periods of delaymay be subjected to wide variations and still keep the operation of thesystem within the principles of this invention as described above.

0! course it is to be understood that this invention is not limited tothe Particular details as describedabove as many equivalents willsuggest themselves to those skilled in the art. For example, someaspects of thisinvention may be ap plied to tubes having other types ofigniting electrodes. Other types of rectifiers and time delay relays maybe utilized. Various other changes and additions may be made to thesystem as disclosed. It is accordingly desired that the appended claimsbe given a broad interpretation commensurate with the scope of theinvention within'the art.

What is claimed is: g

1. In combination, a load circuit, circuit means for connecting saidload circuit to a source of alternating current, a pair ofinversely-connected arc discharge devices interposed in said circuitmeans for controlling the flow of current to said load circuit, each ofsaid are discharge devices comprising an anode, a pool type are cathode,

2., In combination, a load circuit, circuit means for connecting saidload circuit to a source of alternating current, a pair ofinversely-connected arc discharge devices interposed in said circuitmeans for controlling the flow of current to said load circuit, each ofsaid are discharge devices comprising an anode, a pool type are cathode,and an igniting electrode adapted to initiate an are spot on saidcathode, an igniting circuit for supplying each of said ignitingelectrodes with igniting impulses, and means responsive to theappearance of a substantial voltage across said are discharge devicesupon failure of one are discharge device to start conducting current,for deenergising the igniting circuit of the other are discharge device.

3. In combination, a load circuit, circuit means ior connecting saidload circuit to a source of a1- ternating current, a pair ofinversely-connected arc discharge devices interposed in said circuitmeans for controlling the flow of current to said load circuit, each ofsaid are discharge devices comprising an anode, a pool type are cathode,and an -igniting electrode adapted to initiate an are spot on saidcathode, an igniting circuit for supplying each of said ignitingelectrodes with igniting impulses, and means responsive to theappearance of a substantial voltage across said are discharge devices,upon failure of one are discharge device tostart conducting currentduring a half cycle, for preventing the other are dischariedevice fromconducting current.

4. In combination, a load circuit, circuit means for connecting saidload circuit to a source of alternating current, a pair ofinversely-connected arc discharge devices interposed in said circuitmeans for-controlling the flow of current to said load' circuit, each ofsaid are discharge devices comprising an anode, a pool type are cathode,ana'an igniting electrode adapted to initiate an are spot on saidcathode, an igniting circuit for supplying each of said ignitingelectrodes with igniting impulses, and means responsive to theappearance of a substantial voltage across said are discharge devices,upon failure of one are discharge device to start conducting currentduring a half cycle, for deenergizing-the igniting circuits of both aredischarge devices for the succeeding half cycle, and for reenergizingthe igniting circuit of said flrst arc discharge device during thefollowing half cycle.

5. In combination, a load circuit, circuit means for connecting saidload circuit to a source of alternating current,"a pair ofinversely-connected arc discharge devices interposed in said circuitmeans for controlling the flow of current to said load circuit, each 'ofsaid are discharge devices comprising an'anode, a pool type are cathode,and an. igniting electrode adapted to initiate an are spot on saidcathode, an igniting circuit for supplying each of said ignitingelectrodes with igniting impulses," means for energizing said ignltingcircuits from across said discharge devices, whereby the voltageimpulses occurring across said are discharge devices constitute saidigniting impulses, and means responsive to the voltage across said aredischarge devices for dcenergizing the igniting circuit of one of saiddischarge devices when the other of said are discharge de-,

vices fails to fire. I

6. In combination, a load circuit having a power factor less than unity,circuit means for connecting said load circuit to a source ofalternating current, a pair of inversely connected arc discharge devicesinterposed in said circuit means for controlling the flow of current tosaid load circuit, each of said arc discharge devices comprising ananode, a pool type are cathode, and an igniting electrode adapted toinitiate an are spot on said cathode, an igniting circuit for supplyingeach of said igniting electrodes with ignit ing impulses, means forenergizing said igniting circuits from across said discharge devices,whereby the voltage impulses occurring across said arc discharge devicesconstitute said igniting impulses, and means responsive to the voltageacross said are discharge devices for deenergizing the igniting circuitof one of said discharge devices when the other oi said arc dischargedevices ifails to fire. I

7-. In combination, a load circuit having a power factor less thanunity, circuit means for connecting said load circuit to a source ofalternating current, a 'pair of inversely-connected are dischargedevices interposed in said circuit means for controlling the flow ofcurrent to said load circuit, each of said are discharge devicescomprising an anode, a pool type arc'cathode, and an igniting electrodeadaptedito initiate an are spot on said cathode, an igniting circuit forsupplying each of said igniting electrodes with igniting impulses, meansfor energizing said igniting circuits from across said dischargedevices, whereby the voltage impulses occurring across said aredischarge devices constitute said igniting impulses, and meansresponsive to the occurrence of a voltage impulse of substantiallylonger duration than a normal igniting impulse for deenergizing theigniting circuit of one of said discharge devices when the other of saidare discharge devices fails to fire.

8. In combination, a load circuit, circuit means for connecting saidload circuit to a source of alternating current, a pair ofinversely-connected arc discharge devices interposed in said circuitmeans for controlling the flow of current to said load circuit, each ofsaid are discharge devices comprising an anode, a pool type are cathode,and an igniting electrode adapted to initiate an arc spot on saidcathode, an igniting circuit for supplying each of said ignitingelectrodes with igniting impulses, means for energizing said ignitingcircuits from across said discharge devices, whereby the voltageimpulses occurring across said are discharge devices constitute saidigniting impulses, and a relay havlng operating means responsive to thevoltage across said arc discharge devices and circuit-interrupting meansoperated by said relay for deenergizing the igniting circuit of one ofsaid'discharge devices when the other of said arc discharge devicesfails to fire.

9. .In combination, a load circuit having a power factor less thanunity, circuit means for connecting said load-circuit to a source ofalternating current, a pair of inversely-connected arc discharge devicesinterposed in 'said circuit means for controlling the fiow of current tosaid load circuit, each of said are discharge devices comprising ananode, a pool type are cathode, and an igniting electrode adapted toinitiate an are spot on said cathode,'an igniting circuit for supplyingeach of said igniting electrodes with igniting impulses, means forenergizing said igniting circuits from across said' discharge devices,

whereby the voltage impulses occurring across said are discharge devicesconstitute said igniting impulses, and a relay having operating meansresponsive to the occurrence of a voltage impulse of substantiallylonger duration than a normal igniting impulse and circuit-interruptingmeans operated by said relay for deenergizing the ignitmeans forconnecting said load circuit to a source of alternatingcurrent, a pairof inversely-connected arc discharge devices interposed in said circuitmeans for controlling the flow of current curring across said arcdischarge devices constitute said igniting impulses, and meansresponsive to the voltage across said arc discharge devices fordeenergizing the igniting circuit of one of said discharge devices whenthe other of said are discharge devices fails to fire, said means beingdelayed in its deenergizing action beyond the initialapplication of anormal igniting impulse to said other are discharge device.

11. In combination, a load circuit, circuit means for connecting saidload circuit to a source of alternating current, a pair ofinversely-connected arc discharge devices interposed in said circuitmeans for controlling the fiow of current to said load circuit, each ofsaid are discharge devices comprising an anode, a pool type are cathode,and an igniting electrode adapted to initiate an arc spot on saidcathode, an igniting circuit for supplying each of said ignitingelectrodes with igniting impulses, means for energizing said ignitingcircuits from across said discharge devices, whereby the voltageimpulses occurring across said arc discharge devices constitute saidigniting impulses, andmeans respon-- sive to the voltage across said arcdischarge devices for deenergizing the igniting circuits of both of saiddischarge devices when one of said arc discharge devices fails to fire,said means being adapted to reenergize the igniting circuit of thelatter are discharge device during the next cycle following said failureto fire.

12. In combination, a load circuit, circuit means for connecting saidload circuit to a source of alternating current, a pair ofinversely-connected arc discharge devices interposed in said circuitmeans for controlling the fiow of current to said load circuit, each ofsaid are discharge devices comprising an anode, a pool type are cathode,and an igniting electrode adapted to initiate an arc spot on saidcathode, an lgniting circuit for supplying each of said ignitingelectrodes with igniting impulses, means for energizing said ignitingcircuits from across said discharge devices, whereby the voltageimpulses occurring across said arc discharge devices constitute saidigniting impulses, and means responsiv to the voltage across said aredischarge devices for deenergizing the igniting circuits of .both ofsaid discharge devices when one of said nected arc discharge devicesinterposed in said circuit means for controlling the flow of current tosaid load circuit, each of said arc discharge devices comprising ananode, a pool type are cathode, and an igniting electrode adapted toinitiate an arc spot on said cathode, an igniting circuit for supplyingeach of said igniting electrodes with igniting impulses, means forenergizing, said igniting circuits from across said discharge devices,whereby the voltage impulses occurring across said are discharge devicesconstitute said igniting impulses, electro-rnagnetic means included ineach ofv said igniting circuits and adapted to become saturated upon theoccurrence of a voltage impulse of substantially longer duration than anormal igniting impulse,

I and means responsive to the increased current of alternating current,a pair of inversely-connected gas-filled discharge devices interposed insaid circuit means for controlling the flow of current to said loadcircuit, each of said gasfilled discharge devices comprising an anode, acathode, and control means for causing a discharge to be started betweensaid cathode and anode, a control circuit for supplying each of saidcontrol means with discharge starting impulses, and means responsive tothe appearance of a substantial voltage across said discharge devicesupon failure of one discharge device to start conducting current forpreventing the other are discharge device from conducting current.

15. In combination, a load circuit, circuit means for connecting saidload circuit to a source of alternating current, a pair ofinversely-connected gas-filled discharge devices interposed in saidcircuit means for controlling the flow of current to said load circuit,each of said gas-filled discharge devices comprising an anode, aoathode, and control means for causing a discharge to be star-tedbetween said cathode and anode, a control circuit for supplying each ofsaid control means with discharge starting impulses, and meansresponsive to the appearance of a substantial voltage across saiddischarge devices upon failure of one discharge device to startconducting current for deenergizing the control circuit of the other aredischarge device.

' DAVID D. COFFIN.

